This study assessed the evolution of wastewater systems during the rapid urbanization of Beijing, with special focuses on the carbon footprints and growing underground WWTPs (u-WWTPs). Specifically, the Bishui plant (in situ constructed u-WWTP) was assessed in detail regarding eco-environmental benefits. Our results showed that, the direct emission intensity of 65 WWTPs decreased from 0.47 to 0.24 kg CO_2eq/m³, when the electricity intensity increased from 0.22 to 0.39 kWh/m³ from 2010 to 2020. Bishui u-WWTP emitted 36.6 kt CO_2eq/year (0.09 kg CO_2eq/m³), with electricity intensity of 0.43 kg CO_2eq/m³. Additionally, compare to the hypothetical relocating scenario, it saved 6.67 × 10⁴ m² land and 33.0 kt CO_2eq/year, and the created urban river carries 6.5 × 10¹³ J/year heat outside town. The evaluation and balance of choice for conventional or underground WWTP should be made case by case. However, this study demonstrated that u-WWTP is not only a construction manner, but a sustainable management model with positive eco-environment effects, algin with future city expansion, and circular economy visions.

This study reviewed nexus researches, synthesize and discuss insights, methodological practices, and future outlook of water-related energy consumption assessment of the food system. For the first time, the study assessed: (i) the trends and drivers of water-related energy research in different countries, (ii) how water-related energy in the food system is being evaluated (objectives & scale, study dimension & analysis focus, and methods) and (iii) the significance of food-system water-related energy in comparison with other sectors. Of 686 nexus studies undertaken since 1990, 104 studies (15%) quantified water-related energy. Studies have generally broadened in scope through time. The USA, China, and Australia have conducted most studies representing 23%, 17%, 15% of total respectively. A few of the identified major drivers in these countries leading water-related energy assessment are: providing optimal solutions and avoiding problem-shifting, analyzing the challenges and opportunities to reduce water-related energy, and exploring the energy-saving benefits by saving water. Of the 104 water-related energy studies, 65 articles (∼60%) related to the food system, focussed on the agriculture phase for irrigation energy consumption. Existing nexus studies often ignored other phases such as food processing and cooking, which are more energy-intensive. Over 50% of studies used material flow analysis to evaluate water-related energy in the food system. Few of the nexus studies evaluated inter-regional flows or changes through time. Absence of a comprehensive study of the entire food system, and wide variations in study system boundary and definitions, make it difficult to compare sectoral significance. However, the order of sectoral water-related energy consumption (from highest to lowest) identified as industrial, residential, agriculture, and water and wastewater service. Our review demonstrates a tremendous opportunity and need for an overarching framework to enable systematic evaluation and benchmarking of water-related energy consumption of the food system.

This study focused on understanding what sector-region combinations could be targeted to reduce total city water footprints? We used multi-regional input-output analysis of direct and virtual water, across five Australian capital cities and their supporting regions. The key novelty of this study is the high spatial resolution policy-relevant sub-sectoral analysis to identify sector-region combinations to reduce city water footprints. Virtual water footprints were 8-10 times higher than direct water consumption (per capita) in all studied cities. Virtual water from outside the city boundary is almost 20 times higher than the virtual water sourced from within the city boundary in all studied cities. Water-efficiency programs can significantly reduce the virtual water footprints of the studied cities. This includes water-efficiency and recycling on farm, and in food processing (e.g. livestock feed growing, dairy cattle farming, vegetable growing and processing) in rural regions of New South Wales, Queensland, and Victoria. The results are relevant to strategic city water footprints reduction, sustainable sourcing and planning for future disturbance of product supply, and water-sensitive city developments considering both direct and virtual water flows.

Historically, little consideration has been given to water performance of urban developments such as “hydrological naturalness” or “local water self-sufficiency”. This has led to problems with increased stormwater runoff, flooding, and lack of local contributions to urban water security. Architectural design, water servicing technologies and environmental conditions are each known to influence water performance. However, most existing models have overlooked the integration of these factors. In this work, we asked ‘how the water performance of urban developments at site-scale can be quantified, with joint consideration of architectural design, water servicing technologies, and environmental context (i.e. climate and soil)’. Answering this question led to the development of a new method and tool called Site-scale Urban Water Mass Balance Assessment (SUWMBA). It uses a daily urban water mass balance to simulate design-technology-environment configurations. Key features include: (i) a three-dimensional boundary focussed on the “entity” of development (ii) a comprehensive water balance accounting for all urban water flows, (iii) methods that include key variables capturing the interactions of natural, built-environment and socio-technological systems on water performance. SUWMBA's capabilities were demonstrated through an evaluation of a residential infill development case study with alternative design-technology-environment configurations, combining three dwelling designs, seven water technologies and three environmental contexts. The evaluation showed how a configuration can be identified that strikes a balance between the conflicting objectives of achieving the desired dwelling densities whilst simultaneously improving water performance. For two climate zones, the optimal configuration increases the total number of residents by 300% while reducing the imported water per capita and stormwater discharge by 45% and 15%, respectively. We infer that SUWMBA could have strong potential to contribute to performance-based urban design and planning by enabling the water performance of dwelling designs to be quantified, and by facilitating the setting of locally-specific water performance objectives and targets.

Recovering resources from wastewater systems is increasingly being emphasised. Many technologies exist or are under development for recycling nutrients such as nitrogen and phosphorus from wastewater to agriculture. Planning and design methodologies are needed to identify and deploy the most sustainable solutions in given contexts. For the environmental sustainability dimension, life cycle assessment (LCA) can be used to assess environmental impact potentials of wastewater-based nutrient recycling alternatives, especially nitrogen and phosphorus recycling. This review aims to evaluate how well the LCA methodology has been adapted and applied for assessing opportunities of wastewater-based nutrient recycling in the form of monomineral, multimineral, nutrient solution and organic solid. We reviewed 65 LCA studies that considered nutrient recycling from wastewater for agricultural land application. We synthesised some of their insights and methodological practices, and discussed the future outlook of using LCA for wastewater-based nutrient recycling. In general, more studies suggested positive environmental outcomes from wastewater-based nutrient recycling, especially when chemical inputs are minimised, and source separation of human excreta is achieved. The review shows the need to improve methodological consistency (e.g., multifunctionality, fertiliser offset accounting, contaminant accounting), ensure transparency of inventory and methods, consider uncertainty in comparative LCA context, integrate up-to-date cross-disciplinary knowledge (e.g., agriculture science, soil science) into LCA models, and consider the localised impacts of recycled nutrient products. Many opportunities exist for applying LCA at various scales to support decisions on wastewater-based nutrient recycling – for instance, performing “product perspective” LCA on recycled nutrient products, integrating “process perspective” LCA with other systems approaches for selecting and optimising individual recovery processes, assessing emerging nutrient recovery technologies and integrated resource recovery systems, and conducting systems analysis at city, national and global level.

The need for energy in water provision and use is obvious, however the drivers are often complex, difficult to assess, and often inconsistently presented. Here we build a clearer definition and conceptual framework of “water-related energy”. We apply this framework to harmonise data and results across disparate studies so that regional estimates of water-related energy can be compared in a consistent way for the first time. We show how widely different boundaries have been used for analysis including or excluding: water and wastewater utilities, as well as residential, commercial, industrial, and agricultural water users. Consequently, understanding of what constitutes “water-related energy” is widely divergent. We demonstrate how up to 12.6% of total national primary energy use can be influenced by water, when (i) water-related energy of water users, and (ii) energy use by water utilities, are all included. Water heating for residential, commercial, and industrial purposes is the dominant fraction. Water and wastewater utilities use 0.4–2.3% of primary energy or 0.6–6.2% of regional electricity, mostly for water pumping. This is substantial, but lower than frequent claims in the media and reports. To answer how is miscommunication influencing policy? we undertake a novel systematic tracking of communication to demonstrate distortion between research and its application in government reports, media and policy. We show that significant confusion is caused by (i) unclear or inconsistent boundaries (ii) widely differing use of terms for water “system”, “sector”, and “supply”, (iii) frequent failure to distinguish ‘energy’ from ‘electricity’ and (iv) wide use of non-standard units. While acknowledging that media is often less accurate than government reports, and that peer-reviewed articles generally have highest overall quality, we observe miscommunication and inconsistency in all publication forms. We argue a global protocol is needed to improve consistency of analysis and sharpen policy towards sustainable water end use because this is where most water-related energy occurs. We establish a foundational framework and definitions for this protocol while recognising much more needs to be done. The strong practical and theoretical implications of the work for sustainable cleaner production are elucidated. This is timely, as global quantification of water-related energy has yet to occur particularly for water end-use which is the dominant component.